1. Field of the Invention
The present invention relates to a technique for performing printing by recording ink dots on a recording medium while a print head is moving in the main scan direction.
2. Description of the Related Art
Ink jet printers which eject ink from a head and laser printers have become popular as output devices for computers. Especially in recent years, color printers using color inks have also been widely utilized.
Various types of printing media for ink jet printers have been commercially marketed. Since the coloring properties of inks differ in different printing media, there are considerable differences in the images obtained. The type of printing medium used also affects the precision of the sub-scan feed of the printing medium (hereafter referred to as the “paper feed”). For example, the actual feed amount may vary considerably between printing media with easy-slip surfaces and printing media with surfaces that do not slip easily, even if the same feed operation is performed. Furthermore, the precision of the paper feed tends to vary considerably from printer to printer.
The degree of precision of the paper feed has a great effect on the image quality. However, in the case of printers that perform printing using a so-called interlace recording mode, the image quality degradation caused by paper feed error can be suppressed to some extent by appropriately setting the paper feed amount. Here, the term “interlace recording mode” refers to a printing method that is performed using a print head that has nozzles aligned in a row at a nozzle pitch that is twice the dot pitch in the sub-scan direction (i. e., the main scan line pitch) or greater. In cases where such a print head is used, gaps are generated between the main scan lines (raster lines) that are recorded by a single main scan pass. Furthermore, a number of main scan passes that is equal to the number of main scan lines contained in these gaps is further required in order to eliminate the gaps. It is known that various feed amounts can be used in the case of such an interlace recording mode. Conventionally, therefore, the effect of variation in the paper feed precision on the mage quality has be minimized by appropriately selecting the paper feed amount in the interlace recording mode.
For the reasons described above, the direct correction of paper feed error in printers using an interlace recording mode has not been seriously considered. However, as high image quality in printers has spread in recent years, there has been a demand for further improvement of image quality by the appropriate correction of paper feed error in printers that perform printing in an interlace recording mode. This demand has been increased not only against interlace recording mode printers but also against non-interlace recording mode printers.